diff --git a/course-definition.yml b/course-definition.yml
index 391840dd..3a480285 100644
--- a/course-definition.yml
+++ b/course-definition.yml
@@ -252,7 +252,7 @@ stages:
       $ redis-cli get random_key
 
       # Then, it'll wait for the key to expire and send another GET command
-      # The response to this should be `-1\r\n` (a "null bulk string")
+      # The response to this should be `$-1\r\n` (a "null bulk string")
       $ sleep 0.2 && redis-cli get random_key
       ```